The subject matter disclosed herein relates to the art of rotary wing aircraft and, more particularly, to an active rotor blade control effector system for a rotary-wing aircraft.
Control of rotary-wing aircraft is affected by rotor blade pitch variations. The rotor blades are controlled individually (cyclic control) and collectively (collective control). Main rotor pitch control is typically achieved through a swashplate assembly that transfers motion of non-rotating control members to rotating control members. The transfer of motion occurs once per blade revolution (1/rev). Transferring cyclic and collective control inputs only once per revolution provides a limited control input envelope for the rotor blade.
In addition to limiting control inputs to 1/rev, conventional rotor blades, in descent flight conditions, generate noise that is commonly referred to as blade-vortex interactions (BVI) noise or blade slap. BVI noise is generated by blade tip vortices that interact with the rotor blades. BVI events are high frequency unsteady airloads (>15/rev) have been identified as one of the more objectionable noises produced by rotary-wing aircraft, particularly during descent conditions. Rotor blades also generate thickness noise based on their shape, loading, and motion. This noise tends to occur in the plane of the rotor disk and occurs within a frequency range that is easily detected electronically at large distances thus increasing vulnerability of military aircraft. Typically, flap motions of 2/rev-3/rev have been shown to be effective for noise reduction. Additionally, specialized waveforms can potentially reduce thickness noise through pressure cancelation. The deployment of the effector for noise reduction can be determined using a closed-loop feedback controller. Finally, vibrations generated by conventional rotor blades translate to 4/rev and 8/rev in the fixed frame, these contribute heavily to pilot fatigue and mechanical wear. Reduction of vibration level required harmonic control primarily at the frequencies of (n−1)/rev, n/rev, and n+1/rev, where n is the number of blades.
In order to minimize noise and vibration, certain rotor blade systems employ trailing-edge flaps that are deployed during descent flight conditions. Existing trailing-edge flaps designed for this purpose are typically more than 10% of blade chord length in size and are shiftable plus/minus about 0-5 degrees with respect to a freestream direction. The relatively large size of the flaps limits possible actuation speeds and adds significant weight to the rotor blades.